A/C issue?

It was okay, then today i was cleaning it out and noticed it isn't as good, so checked pressure and was more than full. Let Freon out but all that came out was air. Usually, i have seen this, is when moisture ir air is in place of Freon, so let most of it out until compressor stopped, now it won't come in as its low. Fan was working when compressor was on. Saw bunch if relays in engine box but nothing is labeled, want to jump it so i can feed it enough Freon to work on its own. Or can i charge it from high pressure while the engine is off?